This invention relates generally to gates for handling dry bulk material, and more particularly to an orifice gate valve which may be quickly disassembled, cleaned and returned to service.
There are five primary types of shut-off gates or valves used in handling dry bulk materials. These types include: slide knife gates, iris valves, butterfly valves, pinched valves and dome valves. Within the category of slide knife gates there are a number of different kinds of valves. Among the various types of slide knife gate valves are orifice gates, bull or bullet nose gates, square blade gates, and pivot blade gates. Most valves, including the bull or bullet nose slide knife gates, butterfly, pinch and dome valves, used in handling dry bulk material were originally designed to handle high-pressure liquids, gases and slurries. However, these gates or valves are routinely applied in dry material applications, with varying degrees of success. Because they were originally designed for high pressure liquids, many of the above gate valves have inherent design deficiencies incorporated therein when used for handling dry bulk material.
For example, the bull or bullet nose knife gate valves have a circular blade that will wedge or pack material to the sides and ends of the valve body when the gate closes. In other words, open cavities beside the blade exist where dry material can build up, causing material cross contamination. Material cross contamination can include a mixing of colors, a mixing of different compounds, and food spoilage. The open internal cavities existing within the bull or bullet nose knife gate valve are not a great concern when handling non-perishable liquids and gases, but ideally would be eliminated.
The pivoting blade gate valve, or swing valve, operates in a similar fashion to bull or bullet nose gate valves and also has open cavities that make it undesirable for handling food or materials where cross-contamination and cleanability are a concern. Further, the pivoting blade gate valve is structurally heavy, making it difficult to service and clean.
Dome valves have a domed disc which rotates into place to seal off the flow of material. While dome valves have less open cavities than other valves, they are also structurally heavy, making them more difficult to service and clean. Dome valves are also relatively expensive and require more head room to install as compared to other valves.
Pinch valves utilize an air controlled jacket or sleeve and are primarily used for handling slurries. The pinch valves are also structurally heavy and are problematic when the sleeve of the pinch valve wears through. Further, without a self-cleaning sliding action, material can build up on the bladder wall, leading to material cross contamination and spoilage concerns.
Butterfly valves offer the advantage of being relatively inexpensive and relatively clean. However, in a butterfly valve the disk allowing or preventing material flow, when in the open position, partially obstructs material flow and can allow material build up on the disk. This rotating disk can also be problematic as it pinches, rather than shears, material upon closure. This pinching can prevent full closure of the disk when desired. It can therefore be seen that many of the valves or gates currently in use present a number of drawbacks
Orifice gates, such as that disclosed in U.S. Pat. No. 4,221,307 to Peterson, overcome many of the disadvantages of the gates and valves discussed above. More specifically, the orifice gate reduces or eliminates cavities where material can become lodged and remain trapped. Further, the orifice gate utilizes nylon seals which are resistant to abrasion. Because these seals are made from a hard polymer, they will not quickly abrade away as will rubber or soft packing. Moreover, these hard polymer seals are "live loaded" so that the seal is maintained and compensation is provided for wear. This live loading is accomplished by placing a natural or silicone rubber behind the seal to force it into contact with the blade. The orifice gate also offers the advantage of providing a cleaning of the blade upon opening and closing. This cleaning is achieved by the wiping of the blade against the hard polymer seals.
While the orifice gate discussed above overcomes many of the disadvantages of other types of gates and valves used in the handling of dry bulk materials, problems still exist. For example, in food applications, where bacteria or sticky material build up is a concern, cleanability is one of the most important considerations in the design and selection of a valve or gate. In nonfood applications, material cross contamination, such as with colored plastics or chemical compounds, cleanability is also a great concern. Thus far, none of the gates or valves discussed above, including the pre-existing orifice gate, have offered valves which can quickly be disassembled, cleaned and returned to service. For example, to service the prior art orifice gate, it must be completely unbolted, taken apart, cleaned and rebolted and reinstalled. This process is time consuming, due to the number and position of the bolts.
Therefore, an orifice gate is needed which can be quickly disassembled, cleaned and returned to service, while offering all of the existing advantages of an orifice gate.